Until now, a propulsion engine which uses oil as fuel has been generally used in a merchant ship such as a container carrier or a passenger ship. Due to the recent oil price increase, however, more and more ships are employing a propulsion engine which uses liquefied fuel gas, for example, liquefied natural gas (LNG), liquefied petroleum gas (LPG), or dimethyl ether (DME) which is much cheaper than oil. Furthermore, since the price of LNG in the summer season is 50% lower than in the winter season, LNG may be purchased and stored in the summer season. Therefore, LNG has an advantage in terms of price.
A ship having a liquefied-fuel-gas propulsion engine mounted therein includes a fuel tank which is filled with liquefied fuel gas before sailing. Currently, however, there are not so many harbors provided with a liquefied fuel gas storage facility, for example, an LNG terminal. Furthermore, a current liquefied fuel gas storage facility serves only to transfer liquefied fuel gas stored in a liquefied fuel gas carrier to the ground. For safety reasons, the liquefied fuel gas storage facility is generally located in a position remote from a harbor in which a merchant ship such as a container carrier is at anchor in order for loading and unloading. Therefore, the container carrier should sail to the liquefied fuel gas storage facility located in a position remote from the harbor in order to refuel.
In general, a lot of time and efforts are required to anchor a ship. Therefore, moving the ship to a position remote from a harbor for bunkering may be an unproductive operation which requires a lot of time and efforts and an additional cost.